In wheeled vehicle axle/suspension systems for heavy-duty vehicles, it is often desirable to have a lifting feature that raises an axle so tires do not engage a ground or road surface when extra load carrying capabilities are not needed or when the heavy-duty vehicle is being backed-up. The axle is typically in a lifted position when operating the heavy-duty wheeled vehicle in a lightly loaded or empty condition or being backed-up. The axle is lowered when the heavy-duty wheeled vehicle has a gross vehicle weight that requires an extra axle to conform to weight per axle standards, to avoid accelerated tire wear and avoid abnormal load conditions on the axle/suspension system. It is known that when the heavy-duty wheeled vehicle is moving forward, the drag of the tires will cause the axle to steer automatically or “self-steer” in response to turning of the heavy-duty vehicle. This is referred to as a self-steering axle/suspension system. Heavy-duty wheeled vehicles include trucks, trailers, tractor-trailers or semi-trailers, and the tractor-trailers or semi-trailers may be equipped with one or more trailers. There are some jurisdictions that have requirements for operating heavy-duty wheeled vehicles on highways and roadways. These requirements include provisions that heavy-duty wheeled vehicles operate on the highways and roadways in a manner that does not adversely impact infrastructure. Self-steering axle/suspension systems are often used to comply with these requirements.
Self-steering axle/suspension systems for heavy-duty wheeled vehicles are known. The known self-steering axle/suspension systems distribute the gross vehicle weight carried by axles of a heavy-duty wheeled vehicle when a self-steering axle of the self-steering axle/suspension system is in a down or operating position so tires associated with that self-steering axle engage a ground or road surface. When the self-steering axle is in the down or operating position with the tires in contact with a ground or road surface, the self-steering feature provides a mechanism in which the tires may better follow the path of travel while the heavy-duty wheeled vehicle is turning and still help carrying the load of the heavy-duty vehicle. When the heavy-duty wheeled vehicle has little or no load, the self-steering axle can be lifted so the tires do not contact the ground or a road surface.
Self-steering axle/suspension systems, particularly in the medium and heavy-duty truck and semi-trailer industry, are currently popular. The self-steering axle/suspension systems rely on the drag of the tires as the vehicle proceeds in the forward direction to effect self-steering automatically in response to turning of the vehicle. Typical of self-steering axle/suspension systems are those referred to as “trailing” arm suspension systems found on trucks and semi-trailers and include knuckles that enable pivotal movement of an axle spindle relative to an axle central tube. The self-steering axle/suspension systems may be of the liftable or non-liftable type.
Self-steering axle/suspension systems often include air actuated disc brake systems. The air actuated disc brake systems include air operated actuators or brake chambers that are generally mounted behind and below the axle. This location typically prevents the brake chamber from contacting frame members of the heavy-duty vehicle and/or a component of an axle/suspension system. However, such positioning of the actuator or brake chamber exposes it to potential damage by being hit by road debris or even by contacting the ground or road surface over which the heavy-duty vehicle operates. Further limitations, disadvantages and drawbacks associated with the previously known self-steering axle/suspension systems include air actuated disc brake systems are that they have relatively large and relatively heavy upper king pin mounting bosses on knuckles, have relatively large offsets of the king pin from the axle spindle centerline in the direction of movement or travel of the heavy-duty vehicle and positioning the longitudinal mid-point of the king pin in substantially a centered vertical position relative to the axle spindle centerline.
The limitations, disadvantages and drawbacks associated with the prior art self-steering axle/suspension systems incorporating air disc brake systems make it desirable to develop an improved self-steering axle/suspension system for use on a heavy-duty vehicle. The self-steering axle/suspension system of the subject disclosure satisfies the need and overcomes the limitations, disadvantages and drawbacks by including a new and improved knuckle. The new and improved knuckle locates the brake chamber in a position that protects it from potential damage from road debris and ground contact, has an air disc brake actuator that avoids contact with parts of the heavy-duty vehicle during pivotal movement of the knuckle, has relatively smaller offsets of the king pin from the axle spindle centerline and positions the longitudinal mid-point of the king pin vertically below the axle spindle centerline.